In a small saucepan combine the glaze ingredients and whisk until smooth. Bring to a boil over medium-high heat and cook until thickened, 1 to 2 minutes. Keep the glaze warm or reheat when ready to serve.
Prepare the grill for indirect cooking over medium heat (350° to 450°F).
Season both sides of the pineapple slices with the peppercorns. Brush the cooking grates clean. Grill the pineapple over indirect medium heat, with the lid closed as much as possible, until well marked, 6 to 8 minutes, turning once. Remove from the grill and serve each pineapple slice with a scoop of ice cream and some of the glaze drizzled over the top.